The present invention relate to a circuit breaker such as a molded case circuit breaker or an earth leakage breaker having a movable contact opened by an electromagnetic repulsive force when a large current such as a short-circuit current flows. In particular, the present invention relates to a circuit breaker having a protection cover made of an insulating material that covers a movable contact to extinguish a contact arc generated when the contact opens.
A protection cover made of an insulating material for a movable contact in a conventional circuit breaker is disclosed in Patent Reference 1 or 2. According to Patent References 1 and 2, the insulating material is disposed near a contact of the movable contact to improve breaking capability. The insulating material having a shape to cover a periphery of the contact is fixed by clamping with a pin penetrating the contact and the insulating material.
Patent Reference 1: Japanese Patent Publication (Kokai) No. 57-130325
Patent Reference 2: Japanese Patent Publication (Kokai) No. 57-130329
In the circuit breakers disclosed in Patent References 1 and 2, when the protection cover made of the insulating material is disposed to cover the movable contact, the protection cover is pressed against the movable contact by clamping with the pin (or clamping with a bolt). Depending on the material and strength of the protection cover and the pin, the protection cover may break when the pin is clamped with an excessive stress. When the protection cover is loosely fixed and the protection cover is detached as the moving contact repeats opening and closing, the contact arc can not be extinguished upon an over-current, thereby damaging a wiring on a secondary side of the circuit breaker and a connection device.
Also, the arc may be spread through a metal member such as a pin and the like, thereby lowering current limiting capability. When the protection cover is damaged, the protection cover may fall off and obstruct a function of the circuit breaker, thereby damaging a wiring on a secondary side of the circuit breaker.
In view of the foregoing problems, an object of the present invention is to provide a circuit breaker in which a protection cover made of an insulating material covers a movable contact and is difficult to detach without other components causing an adverse effect such as spreading an arc, thereby preventing damage on a wiring on a secondary side of the circuit breaker and a connection device.
Further objects and advantages of the invention will be apparent from the following description of the invention.